Constructing conductive multi-walled carbon nanotubes network inside hexagonal boron nitride network in polymer composites for significantly improved dielectric property and thermal conductivity

With the rapid development of high performance capacitors for energy storage, materials with both giant dielectric constant and low dielectric loss are urgently needed. Adding conductive filler could largely enhance the dielectric constant of polymer matrix but also greatly increase the dielectric loss. In this study, we provide a new strategy by using hybrid fillers to construct a segregated double network, where conductive multi-walled carbon nanotubes (MWCNT) network is wrapped by insulating hexagonal boron nitride (h-BN) network to destroy the continuity of embedded MWCNT network. To do this, pre-fabricated micron-sized PS/MWCNT particles were completely coated by h-BN through π-π interaction. As a result, the MWCNT network inside h-BN network provides good conductivity while h-BN network provides the isolation effect but do not increase the distance between two adjacent MWCNT agglomerations, which together can maintain the high dielectric constant and decrease the dielectric loss. Therefore, a high dielectric constant of 123 is achieved while a relatively low dielectric loss is also kept as 0.36. More importantly, this special structure of segregated double network also leads to obviously enhanced thermal conductivity which is 2.23-fold of that of the composites with randomly dispersed hybrid fillers. This high thermal conductivity is ascribed to the high synergistic efficiency between segregated h-BN network and dense MWCNT network. We believe that these good comprehensive performances promise this structure to offer a unique and effective way to prepare high-performance dielectric materials with not only high dielectric constant and low dielectric loss, but also good capability of heat dissipation.